In GroupWise 8 we used Delegate rules, to delegate mail to another user. This keeps the body of the mail in the body of the delegated mail.
After the upgrade to GroupWise 2012sp1 the delegated mail is actually attached to the mail, so not kept in the body.

Is this a bug, or is there a setting somewhere?

I have confirmed this behavior on a test VM with GW8 and GW2012.